JP2004191331A - Gas sensor for measuring sox - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor for measuring SOx which is superior in response and can detect SOx of a lower concentration. <P>SOLUTION: A sub electrode 12 made of crystalline sulphate containing silver sulfate is formed on one surface of a substrate 11 made of a solid electrolyte material. A first electrode 13 containing silver is formed on the sub electrode 12 is formed. A second electrode 15 is formed on the other surface of the substrate 11. A gas introducing pipe 22 for introducing measuring gas is arranged such that one surface side of the substrate 11 is covered. A silica pipe is used for the gas introducing pipe 22. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is excellent in responsiveness, to SO _x measurement gas sensor capable of detecting a lower concentration of SO _x.
[0002]
[Prior art]
The SO _x measurement gas sensor using a solid electrolyte material has been known a gas sensor shown in Patent Document 1 or Patent Document 2 and the like.
FIG. 7 shows a gas sensor 10 disclosed in Patent Document 1.
Reference numeral 11 denotes a substrate made of yttria-stabilized zirconia ceramics. Reference numeral 12 denotes a sub-electrode made of a crystalline sulfate containing silver sulfate formed on one surface of the substrate 11, reference numeral 13 denotes a first electrode (silver-containing electrode) containing silver formed on the sub-electrode 12, and reference numeral 14 denotes a sub-electrode. A protective film made of platinum, 15 is a second electrode made of platinum or the like formed on the other surface of the base material 11, 16 and 17 are lead wires made of a platinum wire, and 18 covers one surface side of the base material 11. It is a gas introduction pipe for introducing a measurement gas formed by the above method. The gas introduction pipe 18 is formed of the same yttria-stabilized zirconia ceramic as the base material 11 in order to make the thermal expansion coefficient between the gas introduction pipe 18 and the base material 11 uniform.
By introducing the measurement gas into the gas introduction pipe 18, by the electrode reaction between SO _x gas and the electrode occurs, detects the electromotive force between the first electrode 13 and the second electrode 15, The gas amount can be calculated based on the Nernst equation.
[0003]
[Patent Document 1]
JP-A-7-103937 [Patent Document 2]
Japanese Patent Application Laid-Open No. 9-80017
[Problems to be solved by the invention]
However, inventors have noticed that the above-mentioned conventional SO _x measurement gas sensor has the following problems.
That is, a gas sensor having a similar structure for measuring CO _x gas is known. However, in the SO _x measurement gas sensor, the measurement gas is supplied to the gas introduction pipe 18 in comparison with the CO _x measurement gas sensor. , The response time from the introduction of the electromotive force to the generation of the electromotive force is long.
In the conventional of the SO _x measurement gas sensor there is a problem that can not be detected only until the gas content of up to about 1 ppm.
[0005]
The present invention has been made to solve the above problems, it is an object of excellent response, also to provide a SO _x measurement gas sensor capable of detecting a lower concentration of the SO _x .
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the gas sensor for measuring SO _{x according} to the present invention is configured such that a sub-electrode made of a crystalline sulfate containing silver sulfate is formed on one surface of a substrate made of a solid electrolyte material, and the sub-electrode is formed on the sub-electrode. A first electrode containing silver was formed, a second electrode was formed on the other surface of the substrate, and a gas introduction tube for introducing a measurement gas was provided so as to cover one surface of the substrate. The gas sensor is characterized in that a quartz tube is used as the gas introduction tube.
Further, the base material is made of yttria-stabilized zirconia ceramics.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of the gas sensor 20.
The same members as those in the related art shown in FIG. 7 are denoted by the same reference numerals.
The feature of the present embodiment is that a quartz tube is used as the gas introduction tube 22.
It is preferable to use a yttria-stabilized zirconia ceramic for the substrate 11. The quartz tube 22 can be hermetically fixed to the substrate 11 made of yttria-stabilized zirconia ceramics using sealing glass.
[0008]
Although it is conceivable that the sub-electrode 12 is made only of silver sulfate, silver sulfate is expensive and has a low melting point of 654 ° C., so it is preferable to use it by mixing it with another sulfate.
As the sulfate forming the sub-electrode, for example, lithium sulfate, barium sulfate, calcium sulfate, sodium sulfate and the like can be used. By adding these sulfates, the melting point of the sub-electrode as a whole can be increased, and the ionic conductivity in the sub-electrode can be increased, thereby increasing the gas detection sensitivity.
[0009]
Metallic silver is used for the metal electrode 13. When the metal electrode 13 is formed by metallizing a metal paste, it is preferable to add palladium to silver to form the electrode. By adding palladium, the adhesion between the sub electrode 12 and the metal electrode 13 can be improved.
Since silver or silver-palladium used for the metal electrode 13 has excellent reactivity with SO _x gas and easily generates silver ions by SO _x gas, it is necessary to operate the gas sensor even at a relatively low temperature of about 500 to 600 ° C. Becomes possible.
In addition, the surface of the metal electrode 13 is covered with a platinum film to prevent the metal electrode 13 from being sulfided, and to improve the heat resistance when the gas sensor is heated to a high temperature. The second electrode 15 is also preferably formed of platinum.
[0010]
FIG. 2 shows still another embodiment of the gas sensor 20.
The same members as those shown in FIG. 1 are denoted by the same reference numerals.
Also in the present embodiment, a quartz tube is used as the gas introduction tube 22.
A silver-containing electrode 24 serving as a first electrode is formed on the surface of the sub-electrode 12. As shown in FIGS. 3 and 4, the silver-containing electrode 24 is formed by forming a silver plating layer 28 on the surface of a net 26 made of a platinum wire by silver plating. According to the silver-containing electrode 24, the lead wire 16 made of a platinum wire can be connected to the mesh body 26 by welding such as spot welding, and the connection strength between the two can be increased.
[0011]
Platinum 30 formed by thermally decomposing a platinum compound is formed on the joint interface between the sub-electrode 12 and the base material 11. The platinum 30 can be formed by applying, for example, a hexachloroplatinic acid solution as a platinum compound on the surface of the base material 11 and heating it to 300 to 750 ° C. to thermally decompose hexachloroplatinic acid. By keeping this way the presence of platinum on the bonding interface, can reduce the response time of the sensor to SO _x gas concentration change. It is presumed that the reaction at the bonding interface can be promoted by the presence of platinum 30.
[0012]
In the present invention, a quartz tube is used as the gas introduction tube 22 as described above.
If yttria-stabilized zirconia ceramics made of the same material as the base material 11 is used for the gas introduction pipe as in the related art, there is an advantage that cracks and the like can be prevented because the matching of the thermal expansion coefficient can be obtained.
By the way, in the case of these gas introduction tubes made of ceramics, since the ceramic is a fired body, a large number of irregularities are generated on the inner surface of the gas introduction tube, and the surface area is increased.
[0013]
As a result of observation by the inventors, particularly in the case of a gas containing sulfur, the gas is likely to be adsorbed on the uneven surface, and in the early stage of gas introduction, near the inner surface of the gas introduction pipe, the gas is deposited on the inner surface. It is considered that gas is released after the gas is adsorbed and the gas adsorption is saturated. As a result, the time to reach the sensor unit is delayed, and the time until the electromotive force can be measured, that is, the response time is increased. was gotten.
Based on this finding, in order to solve the above-mentioned problem, the present inventors conceived of quartz as a material other than ceramics and having heat resistance and a smooth surface. Response time has been reduced.
[0014]
5, FIG. 1 shows the response characteristics at the time of SO _x gas measurement with the conventional gas sensor 10 shown in the gas sensor 20 and 7 of the present embodiment of FIG.
As is clear from FIG. 5, the gas sensor 20 according to the present embodiment has a shorter response start time and a shorter rise time than the conventional gas sensor 10.
The time required to rise to a voltage up to 90% of the constant voltage takes about 80 seconds in the case of the conventional product, but is reduced to about 40 seconds in the product of the present embodiment by half.
[0015]
FIG. 6 shows the detection limit concentration of SO _x gas. In the case of the conventional gas sensor, the detection limit was about 1 ppm. However, in the present embodiment, it is possible to detect a concentration as low as about 0.3 ppm as shown in the figure.
In the case of the conventional gas sensor, SO _x gas in the case of low concentration, the gas will be hardly adsorbed to the gas introduction tube surface as, was not detected is above in the embodiment It is considered that the reason why the gas concentration can be detected even at a low gas concentration is that almost no gas adsorption occurs on the inner surface of the gas introduction pipe 22.
[0016]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a gas sensor for measuring SO _x that has excellent responsiveness and can detect low-concentration SO _x .
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a gas sensor.
FIG. 2 is an explanatory diagram showing another embodiment of the gas sensor.
FIG. 3 is an explanatory diagram of a silver-containing electrode.
FIG. 4 is an explanatory view of a state where a silver plating layer is formed on a platinum netting.
FIG. 5 is a graph showing a response characteristic of the gas sensor.
FIG. 6 is a graph showing the detection limit of the SO _x gas concentration.
FIG. 7 is an explanatory diagram of a conventional gas sensor.
[Explanation of symbols]
11 base material 12 sub-electrode 13 first electrode (silver-containing electrode)
14 Protective film 15 Second electrode 16, 17 Lead wire 20 Gas sensor 22 Gas inlet tube 24 Silver-containing electrode (first electrode)
26 Net 28 Silver plating layer 30 Platinum

Claims (2)

A sub-electrode made of crystalline sulfate containing silver sulfate is formed on one surface of a substrate made of a solid electrolyte material, a first electrode containing silver is formed on the sub-electrode, and the other surface of the substrate is made. in the second electrode is formed, SO _x measurement gas sensor gas introduction pipe is provided for measuring the gas inlet covers the one surface of the base material,
SO _x measurement gas sensor, wherein a quartz tube is used for the gas inlet tube. SO _x measurement gas sensor according to claim 1, wherein said substrate is characterized by comprising the yttria-stabilized zirconia ceramics.

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